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Old 4th Mar 2012, 08:07
  #790 (permalink)  
HazelNuts39
 
Join Date: Jul 2009
Location: France - mostly
Age: 80
Posts: 1,689
Originally Posted by Machinbird
Process runs like this:

Oh Oh, lost the airspeeds!
Wait, we are in cruise, instructions say do nothing and warn the crew that they may have to take over.
Power table lookup says cruise power for current flight environment is X, set power to X, maintain Normal law.
Monitor airspeeds to see if we can get a valid airspeed.
Airspeeds agree on 90 knots? Not in the acceptable range-disregard.
Airspeeds now say 271 knots. In acceptable range. Advise crew that we are resuming normal control.
End of allowable dead reckoning period (where control would then pass to the crew).
Very attractive at first sight. We just have to settle on a few details of implementation:
(1) Oh Oh, lost the airspeeds! >>> Based on a single speed (the median)?
(2) Wait, we are in cruise, instructions say do nothing and warn the crew that they may have to take over. >>> Do you mean what the system currently does - maintain current pitch and power and sound 'cavalry charge' - or keep A/P and A/THR engaged, so that A/THR will increase power to Max CLB?
(3) Power table lookup says cruise power for current flight environment is X, set power to X, maintain Normal law. >>> Maintain Normal law means maintaining protection for high AoA and overspeed. Both will not function when IAS drops to low value. High AoA thresholds at low IAS are too high for protection at cruise Mach. There will be no stall warning.
(4) Monitor airspeeds to see if we can get a valid airspeed. Airspeeds agree on 90 knots? Not in the acceptable range-disregard. Airspeeds now say 271 knots. In acceptable range. Advise crew that we are resuming normal control. >>> What is the 'acceptable range' ?
(5) End of allowable dead reckoning period (where control would then pass to the crew). >>> What happens here? Isn't the crew always in control within the flight envelope?

P.S.
What I agree with: When the system drops A/P and A/THR, it could initially set pitch and power corresponding to level flight in still air, and maintain wings level.

Last edited by HazelNuts39; 4th Mar 2012 at 09:37. Reason: P.S.
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